The concept of electrostatic separation is well known in the art. For example, in U.S. Pat. No. 3,493,109 to Carta et al. ore particles are charged by triboelectricity. The Carta et al. separator includes a tangentially arranged inlet duct for feeding ore particles into a cyclone. The inner surface of the cyclone is coated with special materials. The dielectric constant or surface work function of these materials is intermediate that of the two species of particles to be separated.
More particularly, physical contact and friction between the particles themselves and the coated inner surface of the separator produces charges of opposite polarity on the two species of particles to be separated. The charged particles are then delivered from the cyclone to a separation chamber including opposing electrodes of opposite polarity. An electric field results which tends to draw the charged particles apart thereby completing the separation process.
Other examples of the electrostatic separation process are disclosed in, for example, U.S. Pat. Nos. 4,482,351 to Kitazawa et al.; 3,941,685 to Singewald et al.; 5,275,631 to Brown et al.; 5,332,562 to Kersey et al. and 5,224,604 to Duczmal et al.
While all of these known apparatus and processes provide for separation of selected particles, it should be appreciated that improvements are still possible. More specifically, prior art apparatus and methods for electrostatic separation of particles generally rely primarily on particle-wall contact to establish the differential charge on the particle surfaces, while only secondarily relying on the incidental particle-particle contact to further aid in establishing the differential charging. This tends to lead to significant wall erosion and substantially shortens the maintenance intervals between wall replacements: generally, a relatively expensive and somewhat time consuming repair.
Further, prior art approaches generally suffer substantial inefficiencies resulting from failure to take full advantage of the separating capabilities created by imparting differing charges on particles to be separated. Accordingly, a need is identified for an improved apparatus and method.